This invention concerns a liquid phase process and an apparatus for the catalytic conversion of hydrocarbons or carbon monoxide in the presence of hydrogen.
Various processes are known for the hydrotreatment of heavy hydrocarbon charges or of carbon monoxide, in the liquid phase, making use of a dispersed catalyst, and particularly a process wherein the catalyst bed is in dispersed or expanded form, the dispersion or expansion being produced by the upward circulation of the liquid phase and/or hydrogen or a hydrogen-containing gas. An example of such a process is the H-oil process for a hydrocarbon liquid charge. This type of process does not provide for a satisfactory use of the catalyst; as a matter of fact, the catalyst withdrawn from the reactor is a mixture of very substantially deactivated catalyst, of moderately deactivated catalyst and of almost new catalyst and the sorting of the catalyst particles according to their deactivation degree is difficult to achieve.
According to an improvement to said technique (catalyst in a dispersed or expanded form), there is used a series of superposed beds of the same type. The fresh catalyst is introduced at the upper stage of the reactor, preferably after a previous sulfiding, while the stages located below contain a catalyst which is the more deactivated as it is at a lower stage. Periodically the catalyst of one stage n is allowed to go down to the next lower stage n+1, while the less used catalyst of the upper stage n-1 passes to the stage n, and similarly for all the stages. The catalyst of the last stage, at the bottom of the reactor, is discharged, while the fresh catalyst is introduced to the first stage No. 1 at the top of the reactor.
This procedure provides for an improvement of the utilization rate of a catalyst before discharge from the reactor. In addition, the fractionation of the reactor in a series of catalyst beds, improves the efficiency of the reactor. The main problem encountered in that type of reactor, concerns the transfer of the catalyst from one stage to the next stage below.
It has first been proposed to allow the catalyst to progressively go down through all the stages, but this has the major disadvantage of mixing, at each stage, a relatively highly active catalyst of stage n with a relatively less active catalyst of stage n+1, which results in a relatively poor use of the catalyst.
It has also been proposed to transfer the catalyst periodically in separated charges or "batches", which obviates partially some of the preceding disadvantages. But any one of these methods requires the use of valves, with or without hydrogen feed to the transfer duct, above the one or more valves. However, the use of such valves, as described for example in U.S. Pat. No. 3,708,420, involves a risk of rapid wear and deterioration of the valve sealing as a result of the possible presence of abrasive catalyst particles on the valve seat. The construction of the reactor with the positioning of the one or more valves inside the reactor poses difficult problems for their control, their maintenance and their replacement when in operation, as a result of the temperature and pressure conditions and of the corrosive action of the reaction medium. The construction of the reactor with the positioning of the one or more valves outside the reactor as indicated in U.S. Pat. No. 3,708,420, makes it necessary to bore holes at regular intervals in the wall of the reactor for the introduction of the valves and such holes are not desirable in the case of reactors operating both at high temperature and under pressure. Moreover, in the case of catalyst transfer through a duct external to the reactor, the charge is no longer in contact with a sufficient amount of catalyst in the main reaction zone, which disturbs the running of the plant. In addition, by-passing a section of the reactor by means of a lateral duct disturbs the pressure distribution and produces siphonages or even discontinues the catalyst fluidization in said section and, in many ways, results in a substantial disturbance of the reactor operation. Finally, the lateral ducts include knees which interfere with the catalyst flow.